Sizing up the Supreme Court after Justice John Paul Stevens retires

His expected exit shouldn't alter the ideological balance, but his role as the senior justice on the liberal side has been pivotal.

Reporting from Washington — The Supreme Court is about to undergo another generational transition, as the senior leader of its liberal wing, John Paul Stevens, is expected to retire this summer and be replaced by a junior justice appointed by President Obama.

For the moment, the front-runners for the nomination, assuming Stevens does announce his retirement after he turns 90 next month, are said by legal insiders to be U.S. Solicitor Gen. Elena Kagan, 49; Judge Diane Wood, 59, of the U.S. 7th Circuit Court of Appeals in Chicago; and Judge Merrick Garland, 57, of the U.S. Court of Appeals for the District of Columbia Circuit.

They were all once law clerks at the Supreme Court for liberal justices, and they have ties to President Clinton. Wood and Garland were Clinton appointees; Kagan worked in the Clinton White House.

None of them would probably change the ideological balance on the court. But neither would any of them quite replace Stevens, simply because of his experience, his gentle persuasiveness and, particularly, his key position as the senior justice on the court's liberal side for the last 16 years.

When the chief justice votes with the majority, he decides who writes the court's opinion.

But if the chief justice does not have a majority, the senior justice in the majority decides who will write the opinion, which can influence the outcome.

"The big impact will be the loss of Justice Stevens' leadership position, which flowed from both his position as senior associate justice and his unique combination of personality and persuasiveness," said Paul D. Clement, formerly the solicitor general in the George W. Bush administration.

"Even if the president can find someone with similar strengths in building coalitions -- and that is a mighty tall order -- the president cannot make the nominee the senior associate justice."

His departure has a "potentially huge impact because Stevens has used that opinion assignment authority with striking effectiveness," said Richard Lazarus, a Georgetown University law professor.

On issues as varied as the death penalty, the Guantanamo Bay military prison, gay rights and global warming, the Stevens wing of the court has prevailed in major rulings.

But his departure would put Justice Anthony M. Kennedy in an even more significant spot.

After Stevens, the senior justice would be Antonin Scalia, a 1986 appointee of President Reagan, but he generally sides with Chief Justice John G. Roberts Jr.

Kennedy, a 1988 Reagan appointee, is next in line.

"Before and after Justice Stevens, it was often the case that if a 'liberal' result is possible, it is because Justice Kennedy is leaning that way," said Walter Dellinger, solicitor general under President Clinton. "But after Stevens, Justice Kennedy will be the senior justice in almost any liberal majority, and he will assign the opinion to himself or another justice. It may even, at the margin, influence how he votes."

Dellinger said that if Kennedy's view of an issue was between that of the four who leaned to the right and four who leaned to the left, he could vote with the liberals and control the result.

"He might honestly believe that he can best achieve a result he believes is legally optimal if he leans left and writes a cautious opinion himself," Dellinger said.

Otherwise, if there is a new leader for the court's liberal wing, it figures to be Justice Ruth Bader Ginsburg. She has become more outspoken in recent years, and she will be next in line for seniority after Kennedy.

Stevens' departure, while not official, is to some a foregone conclusion. He has hired only one clerk for the term that begins in the fall, rather than the usual four, and he has said it is not exactly news that he is long past the normal age for retirement.

If Stevens retires this year, he will probably make an announcement in late April after the justices have heard arguments in the last of their cases for the term.

This would give the White House time to announce a nominee before the summer, and set the stage for confirmation hearings before August.